A cellular network is a radio network made up of a number of radio cells (or just cells) each served by a fixed transmitter, known as a cell site or base station. These cells are used to cover different areas in order to provide radio coverage over a wider area than the area of one cell. Cellular networks include a set of fixed main transceivers each serving a cell and a set of distributed transceivers (which are generally, but not always, mobile) that provide services to the network's users.
There are a number of standards organizations that attempt to develop standards for cellular networks. One example of such a standards organization is the 3rd Generation Partnership Project (3GPP). 3GPP LTE (Long Term Evolution) is the name given to a project within 3GPP to improve the Universal Mobile Telecommunications System (UMTS) standard to cope with future technology evolutions. 3GPP LTE Advanced is currently being standardized by 3GPP as an enhancement of 3GPP LTE.
Coordinated multiple point transmission/reception (CoMP) is considered one of the promising technologies to improve the performance of 3GPP LTE Advanced. One implementation of CoMP is to transmit the information from multiple base stations to a user equipment (UE) resulting in better signal quality at the UE due to the combining capability of the multiple transmissions at the UE.
When an error is detected in a packet, a Negative Acknowledgement (NACK) may be sent back informing the transmitter(s) about the error. Upon receiving the NACK, the transmitter(s) may resend the packet. The retransmitted packet may be combined with the initial transmission at the receiver and may be decoded. If an error is not detected, an Acknowledgement (ACK) may be sent back. Otherwise, another NACK may be sent back and the process may be repeated until the packet is decoded without an error, or the maximum number of retransmission attempts (e.g., as specified in the standard) is reached.
For a retransmission, the transmitter(s) can resend exactly the same packet as in the original transmission. Alternatively, the transmitter(s) can send different versions of the packet. These different versions are indicated by a Redundancy Version (rv) parameter in Release 8 (LTE).